St. Disgusting's Gyratory

Rejoice, citizens of sunny Norwich. Soon the Conduit of Despair known as St Augustine's Street will soon become Unidirectional. It looks as if the pavements are going to be wider, too. Which is good. Because at the moment the layout deters the casual pedestrian, who has to tiptoe along a razor's width of path as juggernauts hurtle past, threatening to suck him or her clean into the road.

Residents of Northern Norwich may be lightly agitated to note that their part of the city is now open countryside.

Video courtesy of the County Council.

Solomon Curve

Everyone knows that Solomon Grundy was born on a Monday, had a few adventures and died on Saturday. But what about the Solomon curve?



The Solomon curve is a fascinating and initially counter-intuitive relationship between speed and the likelihood of collisions. It says that the absolute speed of your vehicle is not the most important determinant of how likely you are to be involved in a crash – the difference in speed between your vehicle and the average speed of the traffic is.

In other words, if everyone is speeding, it may be safer to speed rather than to stick to the speed limit. The explanation is in the number of manoeuvres that are required per unit of time or distance – overtaking, for instance. Thus, a slow tractor is serious hazard because it forces other vehicles into making a manoeuvre. Also, because manoeuvres often happen at slow speeds (like turning into a side road), a turning vehicle (an obvious hazard) has a lower speed than the average for the road.

UK Road Deaths, 1930-2008

The graph shows the number of people killed on UK roads between 1930 and 2008. As you might expect, there is a general decline. The smooth nature of the line from 1930-1980 is due to XL smoothing the data, which is only available for 5-yearly intervals for this period.

Somewhere in the middle there (1983 to be precise) seatbelts were introduced. There is no obvious effect.

Now, when we bear in mind that traffic levels have increased hugely from the beginning of the series to its end, it's obvious that the roads are actually amazingly safe.



If you plot the number of deaths per unit of traffic, a much smoother decline can be seen. If the roads were as dangerous now as they were in 1955, there would be more than ten times more fatalities on the UK's roads.

Rather insanely, globally, more than a million people die on roads each year. This is a rather difficult number to comprehend. More on road safety statistics later.

WHO page on traffic accidents

Data from Department for Transport