[Tagging] Tagging average speed [Was: Re: Residential roads]

[Woll Newall]

I'm talking about speeds that can be consistently measured, whether  
because of consistent rush hour conditions or other factors.

I wouldn't use 'average speed' for the tag, because it implies  
something else, but that's what the OP chose for this thread. 'traffic  
speed' or something like that would be better.

I'm not talking about "the fastest speed you can drive down this  
curving country road", which I agree is going to vary depending on the  
driver etc.

If I go to the nearest main road to my house in between the hours of  
16:00 and 18:00 every weekday, I can measure the speed at which the  
traffic is moving. It will be consistent every day. It will be  
significantly lower than the 'maxspeed' (something like 1/5th  
maxspeed, like 8mph). All of the motor traffic will be travelling at  
this speed (it's so slow that 'slow' drivers will not be left  
behind!). For the rest of the weekday daytime the speed is more  
variable but is also significantly slower than the maxspeed. Only late  
at night/early morning is it physically possible for the traffic to  
get up to the maxspeed.

In UK cities, I expect many roads are like this. As you may imagine,  
using the raw maxspeed for routing (as all the routing systems and  
online routers I have ever used seem to do) is useless in this  
situation. Not only is the 'time to destination' totally incorrect,  
the route chosen is often wrong as well, because choosing a slightly  
different route would make journey times much quicker.

Routing programs can't use heuristics to work out these speeds, they  
are too dependent on local micro-conditions. But we can measure them.

Woll