The Colsterworth junction on the A1 20 years ago was a simple at-grade crossing which unfortunately had attracted a worryingly high accident record. The Highways Agency was rightly concerned and sought ways to overcome this problem.
It was believed that the appropriate solution was a grade separation and, though costly, this would have given many years of service. But the COBA analysis only forecast a limited return based on the then methodology.
As a result, the accountants won and the at-grade roundabout scheme was conceived and built. The cost was further delays to users of the network which, in time, would then justify the hoped for grade separation. It was reckoned that 15-20 years would need to elapse before the final stage could be considered.
If the full analysis had been possible, the cost of the at-grade roundabout would have been saved and the grade separated scheme introduced earlier. A national policy for upgrade of strategic routes would have brought forward one simple junction solution and removed the delays now being faced by present users of the A1.
LESLIE DALBY, firstname.lastname@example.org