Aug 20th 2011, 11:12:25
Trumper, you are correct their is not one national or international code or regulation of signal phase lengths. However, there are industry-wide accepted calculations that are used with a limited degree of variability. A car stopped at a red light, must accelerate and clear the intersection. Depending on the number of lanes per traffic and the expected turning volume, the range will vary from location to location and sometimes even by time of day. Singal engineers are more concerned with network flow and congestion than earning revenue, so the light will be optimized for the lowest theoretical delay to each direction of traffic.
When you are speaking of speed limit cameras, spot cameras are of little use and average speed cameras actual modify driver behaviour. If they have 3 spot cameras within a mile, it sounds like they'd have been better installing an Average Speed Camera system. As such, it would only send out 1 ticket for driving too fast along the path. In your specific area, there is at least a slight history of serious injury with a collision in March 2011. I wasn't able to find a collision database for Maryland off hand, but from the placement, I might suggest they are more politically motivated than safety justified.
Vic, that webpage is too biased to credited. The only references it cites are itself. Vehicles travelling faster than average have the lowest gross rate of accidents, yet the highest severity index. You can have 100 fender-benders at 5-10 mph in stop and go traffic, but it's not as bad as 1 head-on collision at 120 mph net. Engineers are constantly trying to provide a world where we don't kill ourselves by accident, yet we continually push the limits of safety beyond the breaking points.
In traffic engineering findings the vehicles traveling faster than average have the lowest accident rates, yet they are the primary targets of speed enforcement. To this we can now add, with speed limits there was no positive correlation between speed enforcement and accident rates on rural free flowing highways, if anything, the highways became less safe.
Ineffective speed enforcement on rural free-flowing highways has no positive correlation to accident rates, as effective speed enforcement is required to reduce collision fequencies. I don't have references to hand, but the UK has had a number of sucessful trials of average speed cameras for construction sites, reducing the number of tickets issued by a factor of ~80 and collision rate by ~10 from 7-year historic averages.
Also, we are starting to learn sometimes we need to slow down to speed up. Variable Speed Limits on the M25 and M6 around London and Birmingham allow traffic engineers to manage the growth rate of a tailback after a collision, as such they clear the traffic jam faster, and average speeds rise even as people have to drive slower for 10-20km.
That said, with proper regulation of vehicles and drivers, there is no need for a maximum speed limit of segregated 6-lane highways built to a sufficient standard.