http://www.strongtowns.org/journal/2...-engineer.html
Excerpt ...
When the public and politicians tell engineers that their top priorities are safety and then cost, the engineer's brain hears something completely different. The engineer hears, "Once you set a design speed and handle the projected volume of traffic, safety is the top priority. Do what it takes to make the road safe, but do it as cheaply as you can." This is why engineers return projects with asinine "safety" features, like pedestrian bridges and tunnels that nobody will ever use, and costs that are astronomical.
An engineer designing a street or road prioritizes the world in this way, no matter how they are instructed:
1.Traffic speed
2.Traffic volume
3.Safety
4.Cost
The rest of the world generally would prioritize things differently, as follows:
1.Safety
2.Cost
3.Traffic volume
4.Traffic speed
In other words, the engineer first assumes that all traffic must travel at speed. Given that speed, all roads and streets are then designed to handle a projected volume. Once those parameters are set, only then does an engineer look at mitigating for safety and, finally, how to reduce the overall cost (which at that point is nearly always ridiculously expensive).