Road Crossing I — Scratch L2 Lesson 33

Learnt28 min · the rows, lanes of clones, the hop, the hit
Basic24 min · build the first crossing
Challenge 1–327 min · hop, fill the road, get home
Extrabonus · count the cars on the road

WHAT IT SHOULD LOOK LIKE

A new game. Hop the frog from the pavement to the far bank. Three lanes of cars are in the way.

the plan

hit by a car

faded sprite = where it ends up · panels run left to right

Review — the Times-Table Challenge 5 min

(pick random (2) to (12)) made a new question every time.
A timer counted down, and the game ended at zero.
A streak counted right answers in a row.
A wrong answer set the streak back to 0.

Quick-fire

Your streak is 7. You get one wrong. Which block runs?

Reveal the answer

set [streak v] to (0). The streak goes back to where it started. Today a frog does the same thing: when a car hits it, it goes back to the start.

Today’s Topic 3 min

A game drawn as rows
One Car sprite, many clones, three lanes
A clone that drives across and deletes itself
A frog that hops one row per key press
Hit by a car? Back to the start.

Learning outcome

By the end of this lesson you will be able to:

Fill three lanes with clones of one sprite.
Make each clone drive across and delete itself at the edge.
Make a sprite hop one row per key press, and go back to the start when hit.

Learnt — a road full of clones 28 min

The game, as rows

This game is built on a grid. The ground is nine rows. Each row is 40 steps tall. One hop moves the frog one row.

WHAT IT SHOULD LOOK LIKE

Nine rows, each 40 steps tall. One hop moves the frog one row. The numbers are each row's y.

the ground, row by row

Row	y	What is there
Far bank	160	Where the frog wants to go.
Park	120, 80, 40	Safe grass. In Lesson 2-35 it becomes a river.
Sandy strip	0	Safe. A place to rest.
Road	−40, −80, −120	Three lanes of cars.
Pavement	−160	Where the frog starts.

One Car, many clones

You met clones in the Shooting Game. One sprite made every bullet and every zombie. Today one Car sprite makes all the traffic.

A clone is born as a copy of its parent. It starts in the same place, with the same costume and the same size. So the parent goes to the lane first, then makes the clone.


when flag clicked
hide
set size to (40) %

The parent hides. You only ever see its clones.

Then one stack for each lane. They are the same stack with two numbers changed:


when flag clicked
forever
  go to x: (-230) y: (-120)
  create clone of [myself v]
  wait (2) seconds
end

Lane 1


when flag clicked
forever
  go to x: (-230) y: (-80)
  create clone of [myself v]
  wait (3) seconds
end

Lane 2


when flag clicked
forever
  go to x: (-230) y: (-40)
  create clone of [myself v]
  wait (2.5) seconds
end

Lane 3

The y picks the lane. The wait picks the gap between cars. Different waits make the lanes feel different.

Drive across, then delete

Every clone runs this stack the moment it is born:


when I start as a clone
switch costume to (pick random (1) to (3))
show
repeat until <(x position) > (235)>
  change x by (3)
end
delete this clone

Pick a costume, show up, drive right until off the edge, then vanish.

switch costume to (pick random (1) to (3)) — drop the green Operators block into the costume slot. Each car gets a green car, a truck or a purple car.
show — the parent was hidden, so the clone was born hidden too.
repeat until <(x position) > (235)> drives it until it has left the road.
delete this clone — it is gone for good.

WHAT IT SHOULD LOOK LIKE

One hidden Car sprite makes every car. Each clone is born at the left end of its lane, then drives right.

the parent, hidden

a few seconds later

dashed outline = not on the Stage yet · panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the lanes fill, then use ↺ Reset to run it again.

One hidden Car sprite, three lane stacks, and a clone stack. Watch the three lanes fill, each with its own gaps.

Watch out! Forget delete this clone and the cars pile up past the right edge. Scratch stops making clones at 300. After a few minutes your road goes quiet, and nothing tells you why.

The hop

In the Car Race you drove with key [up arrow v] pressed? inside a forever loop. That was right for a car. A car keeps moving while you hold the key.

A frog is different. One tap is one hop. So the frog uses the Events hat instead.


when [up arrow v] key pressed
change y by (40)

✅ One tap, one row.


forever
  if <key [up arrow v] pressed?> then
    change y by (40)
  end
end

❌ Hold it, and the frog shoots off the top.

WHAT IT SHOULD LOOK LIKE

A hat block hops once for each tap. A key check inside a forever loop hops every frame you hold it.

when [up arrow] key pressed · tap once

key pressed? in a forever loop · hold

faded sprite = where it ends up · panels run left to right

Now all four arrows. Up and down each ask a question first:


when [up arrow v] key pressed
if <(y position) < (160)> then
  change y by (40)
end

Not past the far bank.


when [down arrow v] key pressed
if <(y position) > (-160)> then
  change y by (-40)
end

Not below the pavement.


when [left arrow v] key pressed
change x by (-40)

Left.


when [right arrow v] key pressed
change x by (40)

Right.

Without the two if <> then blocks, the frog could hop off the grid. Then every row after that is a little bit wrong.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog one row at a time.

Just the frog. Watch the y box: every hop changes it by exactly 40. At the top and the bottom it stops.

Hit! Back to the start

The frog keeps asking one question. When the answer is yes, it goes home to the pavement.


when flag clicked
go to x: (0) y: (-160)
forever
  if <touching [Car v]?> then
    go to x: (0) y: (-160)
  end
end

touching [Car v]? is true for ANY clone of Car. You do not have to name them.

WHAT IT SHOULD LOOK LIKE

The frog asks one question, over and over: am I touching a car?

hops into the truck

back on the pavement

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog across the road.

The first playable crossing. Hop between the cars. Get hit and you are back on the pavement.

A hidden sprite is never touched. The parent Car sits hidden at the start of a lane. The frog can hop right over it and nothing happens. Only the clones, which show, can hit you.

Basic — build the first crossing 24 min

Start a new project. Build in this order, and test after every step.

Step 1 — paint the ground

Click the Stage, then the Backdrops tab. Use the rectangle tool.
Paint a pale pavement strip along the bottom.
Paint a wide grey road above it — three lanes tall.
Add a sandy strip, then green grass, then a darker far bank at the top.
Draw white dashes between the lanes, if you like.

It does not have to be exact. The lanes need to sit near y = −120, −80 and −40.

Step 2 — the Frog

Choose a Sprite → Frog. Set its size to 45.
Add the four hop stacks from above.
Tap each arrow. Every tap should move one row, and only one.

Step 3 — the Car

Choose a Sprite → Convertible 2. Rename it Car.
In the Costumes tab, choose a costume → Truck-a. Choose another → Convertible. Now Car has three costumes.
Keep that order: green car, truck, purple car. Lesson 2-34 needs it.
Add the setup stack: hide, and size 40.

Step 4 — one lane

Build the Lane 1 stack.
Build the clone stack.
Click the flag. Cars should drive along the bottom lane and vanish on the right.

Step 5 — three lanes

Right-click the Lane 1 stack → Duplicate. Do it twice.
Change the y to −80 and −40. Change the waits to 3 and 2.5.

Step 6 — the hit

Add the frog’s forever stack.
Hop into a car on purpose. The frog should jump back to the pavement.

Step 7 — play it

Cross five times. If it is too easy, make the waits shorter. Too hard? Make them longer.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog across the road.

What you are aiming at. Three lanes of traffic, and a frog that goes back to the start when hit.

No cars appear at all.

The clone stack has no show. The parent is hidden, so every clone is born hidden too.

The frog flies to the top when I hold ↑.

You used key [up arrow v] pressed? in a forever loop. Use the hat when [up arrow v] key pressed instead.

The cars stop coming after a few minutes.

A clone is not deleting itself. Check delete this clone is under the repeat, not inside it.

The frog goes back to the start when nothing hit it.

The parent Car is visible. Make sure the setup stack says hide.

CHALLENGE 1 · L2-33-M1🪙 30 Adcoins8 min

Hop, never fly

All four arrows hop the frog exactly one row or one step of 40.
Holding a key never sends the frog flying.
The frog cannot hop below the pavement or above the far bank.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — eight taps of ↑ from the pavement to the far bank. A ninth does nothing.

start

the far bank · tap ↑ again

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog one row at a time.

The target. Count the taps from the pavement to the far bank.

Done when: eight taps of ↑ take the frog from the pavement to the far bank, a ninth does nothing, and ↓ at the start does nothing.

CHALLENGE 2 · L2-33-M2🪙 50 Adcoins9 min

Three lanes of traffic

One Car sprite. Everything you see is a clone.
Three lanes, each with its own gap between cars.
Cars never stop coming, and none get stuck at the edge.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — three busy lanes, each with its own gaps.

traffic that never stops

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the lanes fill, then use ↺ Reset to run it again.

The target. Three lanes, three different gaps, and it runs for ever.

Done when: you let it run for two minutes, and cars are still coming in all three lanes at the end.

Teacher reveal — the Car sprite


when flag clicked
hide
set size to (40) %

when flag clicked
forever
  go to x: (-230) y: (-120)
  create clone of [myself v]
  wait (2) seconds
end

when I start as a clone
switch costume to (pick random (1) to (3))
show
repeat until <(x position) > (235)>
  change x by (3)
end
delete this clone

Plus two more lane stacks at y −80 and −40. The trap is the gap: a wait shorter than about 1.5 seconds puts a truck on top of the car in front. Let pupils find that by trying it.

CHALLENGE 3 · L2-33-M3🪙 70 Adcoins10 min

Back to the start — or home

A car sends the frog back to the pavement.
Reaching the far bank makes the frog say something.
Then the frog goes back to the pavement to cross again.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a car sends you back. The far bank says well done, then sends you back too.

on the far bank

a second later

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog to the far bank.

The target. Cross the road and the park. On the far bank the frog cheers, then starts again.

Done when: you get hit on purpose and land on the pavement, then cross all the way and hear from the frog on the far bank.

Teacher reveal — a second forever stack


when flag clicked
forever
  wait until <(y position) > (140)>
  say [Made it!] for (1) seconds
  go to x: (0) y: (-160)
end

A second stack on the frog, so the hit loop stays short. The test is <(y position) > (140)>, not = 160: a frog pushed a pixel or two off the grid still counts.

EXTRA MISSION · L2-33-MX🪙 100 Adcoinsbonus

Rush-hour counter

How many cars are on the road right now? Make the game count them, live, on the Stage.

A variable shows the number of cars on the road.
It goes up when a car appears, and down when a car leaves.
It is 0 every time you click the flag.

WHAT IT SHOULD LOOK LIKE

Extra Mission — a number that counts the cars on the road right now.

rush hour

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog. Watch the cars on road box.

The counter goes up and down all game. It never climbs and climbs — that would mean clones are not being deleted.

Teacher reveal


when flag clicked
hide
set size to (40) %
set [cars on road v] to (0)

when I start as a clone
change [cars on road v] by (1)
switch costume to (pick random (1) to (3))
show
repeat until <(x position) > (235)>
  change x by (3)
end
change [cars on road v] by (-1)
delete this clone

cars on road must be For all sprites: every clone adds to the same box. A pupil who puts the −1 below the delete sees the number climb for ever — a deleted clone runs nothing, not even the next block.

Summary 5 min

A grid of 40-step rows keeps every hop in the middle of a lane.
A clone is born as a copy of its parent: same place, costume and size.
So the parent goes to the lane first, then makes the clone.
A clone drives with repeat until <>, then delete this clone.
A hop is a hat block. A drive is a forever loop.
touching [Car v]? is true for every clone of Car.

Clone: A copy of a sprite, made while the game runs.
Parent: The sprite that made the clone. Here it hides.
Lane: One row of the road. Its y tells a car where to drive.
Hop: One jump of exactly one row, one per key press.

Hand in

Share your crossing and send the link to your teacher. Next lesson every lane gets its own speed — and one lane drives the other way.

Learnt28 min · the rows, lanes of clones, the hop, the hit
Basic24 min · build the first crossing
Challenge 1–327 min · hop, fill the road, get home
Extrabonus · count the cars on the road

WHAT IT SHOULD LOOK LIKE

A new game. Hop the frog from the pavement to the far bank. Three lanes of cars are in the way.

the plan

hit by a car

faded sprite = where it ends up · panels run left to right

Review — the Times-Table Challenge 5 min

(pick random (2) to (12)) made a new question every time.
A timer counted down, and the game ended at zero.
A streak counted right answers in a row.
A wrong answer set the streak back to 0.

Quick-fire

Your streak is 7. You get one wrong. Which block runs?

Reveal the answer

set [streak v] to (0). The streak goes back to where it started. Today a frog does the same thing: when a car hits it, it goes back to the start.

Today’s Topic 3 min

A game drawn as rows
One Car sprite, many clones, three lanes
A clone that drives across and deletes itself
A frog that hops one row per key press
Hit by a car? Back to the start.

Learning outcome

By the end of this lesson you will be able to:

Fill three lanes with clones of one sprite.
Make each clone drive across and delete itself at the edge.
Make a sprite hop one row per key press, and go back to the start when hit.

Learnt — a road full of clones 28 min

The game, as rows

This game is built on a grid. The ground is nine rows. Each row is 40 steps tall. One hop moves the frog one row.

WHAT IT SHOULD LOOK LIKE

Nine rows, each 40 steps tall. One hop moves the frog one row. The numbers are each row's y.

the ground, row by row

Row	y	What is there
Far bank	160	Where the frog wants to go.
Park	120, 80, 40	Safe grass. In Lesson 2-35 it becomes a river.
Sandy strip	0	Safe. A place to rest.
Road	−40, −80, −120	Three lanes of cars.
Pavement	−160	Where the frog starts.

One Car, many clones

You met clones in the Shooting Game. One sprite made every bullet and every zombie. Today one Car sprite makes all the traffic.

A clone is born as a copy of its parent. It starts in the same place, with the same costume and the same size. So the parent goes to the lane first, then makes the clone.


when flag clicked
hide
set size to (40) %

The parent hides. You only ever see its clones.

Then one stack for each lane. They are the same stack with two numbers changed:


when flag clicked
forever
  go to x: (-230) y: (-120)
  create clone of [myself v]
  wait (2) seconds
end

Lane 1


when flag clicked
forever
  go to x: (-230) y: (-80)
  create clone of [myself v]
  wait (3) seconds
end

Lane 2


when flag clicked
forever
  go to x: (-230) y: (-40)
  create clone of [myself v]
  wait (2.5) seconds
end

Lane 3

The y picks the lane. The wait picks the gap between cars. Different waits make the lanes feel different.

Drive across, then delete

Every clone runs this stack the moment it is born:


when I start as a clone
switch costume to (pick random (1) to (3))
show
repeat until <(x position) > (235)>
  change x by (3)
end
delete this clone

Pick a costume, show up, drive right until off the edge, then vanish.

switch costume to (pick random (1) to (3)) — drop the green Operators block into the costume slot. Each car gets a green car, a truck or a purple car.
show — the parent was hidden, so the clone was born hidden too.
repeat until <(x position) > (235)> drives it until it has left the road.
delete this clone — it is gone for good.

WHAT IT SHOULD LOOK LIKE

One hidden Car sprite makes every car. Each clone is born at the left end of its lane, then drives right.

the parent, hidden

a few seconds later

dashed outline = not on the Stage yet · panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the lanes fill, then use ↺ Reset to run it again.

One hidden Car sprite, three lane stacks, and a clone stack. Watch the three lanes fill, each with its own gaps.

Watch out! Forget delete this clone and the cars pile up past the right edge. Scratch stops making clones at 300. After a few minutes your road goes quiet, and nothing tells you why.

The hop

In the Car Race you drove with key [up arrow v] pressed? inside a forever loop. That was right for a car. A car keeps moving while you hold the key.

A frog is different. One tap is one hop. So the frog uses the Events hat instead.


when [up arrow v] key pressed
change y by (40)

✅ One tap, one row.


forever
  if <key [up arrow v] pressed?> then
    change y by (40)
  end
end

❌ Hold it, and the frog shoots off the top.

WHAT IT SHOULD LOOK LIKE

A hat block hops once for each tap. A key check inside a forever loop hops every frame you hold it.

when [up arrow] key pressed · tap once

key pressed? in a forever loop · hold

faded sprite = where it ends up · panels run left to right

Now all four arrows. Up and down each ask a question first:


when [up arrow v] key pressed
if <(y position) < (160)> then
  change y by (40)
end

Not past the far bank.


when [down arrow v] key pressed
if <(y position) > (-160)> then
  change y by (-40)
end

Not below the pavement.


when [left arrow v] key pressed
change x by (-40)

Left.


when [right arrow v] key pressed
change x by (40)

Right.

Without the two if <> then blocks, the frog could hop off the grid. Then every row after that is a little bit wrong.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog one row at a time.

Just the frog. Watch the y box: every hop changes it by exactly 40. At the top and the bottom it stops.

Hit! Back to the start

The frog keeps asking one question. When the answer is yes, it goes home to the pavement.


when flag clicked
go to x: (0) y: (-160)
forever
  if <touching [Car v]?> then
    go to x: (0) y: (-160)
  end
end

touching [Car v]? is true for ANY clone of Car. You do not have to name them.

WHAT IT SHOULD LOOK LIKE

The frog asks one question, over and over: am I touching a car?

hops into the truck

back on the pavement

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog across the road.

The first playable crossing. Hop between the cars. Get hit and you are back on the pavement.

A hidden sprite is never touched. The parent Car sits hidden at the start of a lane. The frog can hop right over it and nothing happens. Only the clones, which show, can hit you.

Basic — build the first crossing 24 min

Start a new project. Build in this order, and test after every step.

Step 1 — paint the ground

Click the Stage, then the Backdrops tab. Use the rectangle tool.
Paint a pale pavement strip along the bottom.
Paint a wide grey road above it — three lanes tall.
Add a sandy strip, then green grass, then a darker far bank at the top.
Draw white dashes between the lanes, if you like.

It does not have to be exact. The lanes need to sit near y = −120, −80 and −40.

Step 2 — the Frog

Choose a Sprite → Frog. Set its size to 45.
Add the four hop stacks from above.
Tap each arrow. Every tap should move one row, and only one.

Step 3 — the Car

Choose a Sprite → Convertible 2. Rename it Car.
In the Costumes tab, choose a costume → Truck-a. Choose another → Convertible. Now Car has three costumes.
Keep that order: green car, truck, purple car. Lesson 2-34 needs it.
Add the setup stack: hide, and size 40.

Step 4 — one lane

Build the Lane 1 stack.
Build the clone stack.
Click the flag. Cars should drive along the bottom lane and vanish on the right.

Step 5 — three lanes

Right-click the Lane 1 stack → Duplicate. Do it twice.
Change the y to −80 and −40. Change the waits to 3 and 2.5.

Step 6 — the hit

Add the frog’s forever stack.
Hop into a car on purpose. The frog should jump back to the pavement.

Step 7 — play it

Cross five times. If it is too easy, make the waits shorter. Too hard? Make them longer.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog across the road.

What you are aiming at. Three lanes of traffic, and a frog that goes back to the start when hit.

No cars appear at all.

The clone stack has no show. The parent is hidden, so every clone is born hidden too.

The frog flies to the top when I hold ↑.

You used key [up arrow v] pressed? in a forever loop. Use the hat when [up arrow v] key pressed instead.

The cars stop coming after a few minutes.

A clone is not deleting itself. Check delete this clone is under the repeat, not inside it.

The frog goes back to the start when nothing hit it.

The parent Car is visible. Make sure the setup stack says hide.

CHALLENGE 1 · L2-33-M1🪙 30 Adcoins8 min

Hop, never fly

All four arrows hop the frog exactly one row or one step of 40.
Holding a key never sends the frog flying.
The frog cannot hop below the pavement or above the far bank.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — eight taps of ↑ from the pavement to the far bank. A ninth does nothing.

start

the far bank · tap ↑ again

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog one row at a time.

The target. Count the taps from the pavement to the far bank.

Done when: eight taps of ↑ take the frog from the pavement to the far bank, a ninth does nothing, and ↓ at the start does nothing.

CHALLENGE 2 · L2-33-M2🪙 50 Adcoins9 min

Three lanes of traffic

One Car sprite. Everything you see is a clone.
Three lanes, each with its own gap between cars.
Cars never stop coming, and none get stuck at the edge.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — three busy lanes, each with its own gaps.

traffic that never stops

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the lanes fill, then use ↺ Reset to run it again.

The target. Three lanes, three different gaps, and it runs for ever.

Done when: you let it run for two minutes, and cars are still coming in all three lanes at the end.

Teacher reveal — the Car sprite


when flag clicked
hide
set size to (40) %

when flag clicked
forever
  go to x: (-230) y: (-120)
  create clone of [myself v]
  wait (2) seconds
end

when I start as a clone
switch costume to (pick random (1) to (3))
show
repeat until <(x position) > (235)>
  change x by (3)
end
delete this clone

Plus two more lane stacks at y −80 and −40. The trap is the gap: a wait shorter than about 1.5 seconds puts a truck on top of the car in front. Let pupils find that by trying it.

CHALLENGE 3 · L2-33-M3🪙 70 Adcoins10 min

Back to the start — or home

A car sends the frog back to the pavement.
Reaching the far bank makes the frog say something.
Then the frog goes back to the pavement to cross again.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a car sends you back. The far bank says well done, then sends you back too.

on the far bank

a second later

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog to the far bank.

The target. Cross the road and the park. On the far bank the frog cheers, then starts again.

Done when: you get hit on purpose and land on the pavement, then cross all the way and hear from the frog on the far bank.

Teacher reveal — a second forever stack


when flag clicked
forever
  wait until <(y position) > (140)>
  say [Made it!] for (1) seconds
  go to x: (0) y: (-160)
end

A second stack on the frog, so the hit loop stays short. The test is <(y position) > (140)>, not = 160: a frog pushed a pixel or two off the grid still counts.

EXTRA MISSION · L2-33-MX🪙 100 Adcoinsbonus

Rush-hour counter

How many cars are on the road right now? Make the game count them, live, on the Stage.

A variable shows the number of cars on the road.
It goes up when a car appears, and down when a car leaves.
It is 0 every time you click the flag.

WHAT IT SHOULD LOOK LIKE

Extra Mission — a number that counts the cars on the road right now.

rush hour

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the Stage once and tap ↑ ↓ ← → to hop the Frog. Watch the cars on road box.

The counter goes up and down all game. It never climbs and climbs — that would mean clones are not being deleted.

Teacher reveal


when flag clicked
hide
set size to (40) %
set [cars on road v] to (0)

when I start as a clone
change [cars on road v] by (1)
switch costume to (pick random (1) to (3))
show
repeat until <(x position) > (235)>
  change x by (3)
end
change [cars on road v] by (-1)
delete this clone

Summary 5 min

A grid of 40-step rows keeps every hop in the middle of a lane.
A clone is born as a copy of its parent: same place, costume and size.
So the parent goes to the lane first, then makes the clone.
A clone drives with repeat until <>, then delete this clone.
A hop is a hat block. A drive is a forever loop.
touching [Car v]? is true for every clone of Car.

Clone: A copy of a sprite, made while the game runs.
Parent: The sprite that made the clone. Here it hides.
Lane: One row of the road. Its y tells a car where to drive.
Hop: One jump of exactly one row, one per key press.

Hand in

Share your crossing and send the link to your teacher. Next lesson every lane gets its own speed — and one lane drives the other way.