Letter: Traffic folly

Rush-hour commuters over the Forth road bridge will smile wryly at the ability of an "intelligent transport system" to electronically alter speed limits "to as low as 40mph …to ease congestion" (your report, 11 June). Drivers are intelligently doing that at present by themselves, and at lower speeds.

Any perturbation in traffic flow creates a wave effect, which progresses back along the queue. With ITS, the hope is that application of mathematical wave theory, by using lots of signs to modify speeds by different rates at different points in the queue, can eliminate, or at least attenuate, these waves and keep all traffic moving at a constant speed.

Drivers however, being human, are not electronically controlled so it will be interesting to see if this expensive proliferation of signs proves a success.

A better solution would have been to double the number of lanes from M90 Junction 2a to connect with the existing A823 (M) and the new bridge built as a basic estuary crossing with one short main span over the Grangemouth channel connecting to the M9. That would have doubled the number of lanes over the Forth, once the existing bridge cables were sorted, and made an ITS system unnecessary.

JOHN DUNCAN

Rose Street North Lane

Edinburgh