Tunnels, bridges and roads above or below

A crossing is not always a junction

When one road passes above or below another, there may be no legal or physical connection at the crossing point. Follow the map until a genuine junction or ramp is shown.

Plan the approach before the structure

For a tunnel or bridge route, identify how you enter the structure and where you emerge. The correct crossing can still be reached by the wrong approach road.

Do not cut across flyover geometry

Roundabouts and flyovers should be followed through their actual carriageway layout. Drawing a straight line through the centre can hide an important route mistake.

Practise with several structures

The PCO Topography Pro bank includes routes involving structures such as Rotherhithe Tunnel, Blackwall Tunnel and Limehouse Link, alongside other bridge and grade-separated exercises.

Common mistakes when working on grade-separated structures

A common mistake is trying to solve grade-separated structures too quickly. Candidates can recognise the general area yet miss the first important restriction or connection. Slow the decision down long enough to explain why the first road choice works. That small pause is usually cheaper than repairing several later turns after the route has already moved away from the best corridor.

Another mistake is treating every visible difference from the accepted line as the same problem. With grade-separated structures, the useful question is whether the road sequence is wrong or the drawing is merely imprecise. PCO Topography separates those signals so you can prioritise distinguishing a visual crossing from a real vehicle connection. A route-choice correction should come before cosmetic line placement.

Finally, avoid memorising the shape of one map. Repeat the underlying decision on a different exercise. If you can explain the rule and apply it elsewhere, the skill is becoming transferable. That is why the route bank combines focused practice with full routes rather than asking you to repeat one screenshot until it looks familiar.

A practical study drill for grade-separated structures

Use a three-pass drill. On pass one, inspect the map without plotting and say the likely corridor aloud or write it down. On pass two, plot and submit normally. On pass three, review the first meaningful divergence from the accepted model and state the reason for it in one sentence. This keeps the session focused on decisions instead of random repetition.

For the next attempt, change only the behaviour that caused the main error. If the issue was direction, check arrows earlier. If it was a structure, verify the actual connection. If it was road position, keep the same route choice and place the line more carefully. This controlled correction makes score changes easier to interpret.

Finish by transferring the skill into bridge, tunnel and flyover drills. Do not require a perfect score before progressing; require that you can identify what you did, why it was correct or incorrect, and what you would check on an unfamiliar map. That is a stronger preparation habit than simply accumulating completed route numbers.

• Scan before clicking
• Choose the corridor
• Check direction and restrictions
• Plot meaningful junction points
• Submit without revealing the answer
• Review the first major divergence
• Repeat the same skill on a different route