Traffic  Across  Bridges

October 2002    Back to Bridges    back to Home page

What determines the amount of traffic across a bridge?  Clearly, it is greater than the traffic that preceded the building of the bridge, except in cases where a ferry or a ford was already available.  But does the very presence of the bridge itself influence changes in the neighbourhood which contribute to increased traffic?  If so, what makes this happen?

Here is a diagram showing the density of traffic on some well known bridges, in order of span, longest at the top.  The graph is not very exact, as the data were taken from a number of different sources, but the overall picture is probably qualitatively correct.

Why do you think that the Humber bridge, once the longest span, still carries so little traffic?  Do you think that the density of traffic is the sole criterion of the benefits of a bridge?  What about the examples where the time of the journey has been reduced greatly, because the previous route was either a long detour by road, or a ferry, with all the delays caused by loading and unloading?  What would happen to land values and property values on the other side of a bridge which connects the land to a nearby city?

Do you think that an interesting school project would be to consider a number of bridges, and to look at the density of traffic in each year since the bridges were opened?  What would you expect to find?