How many traffic lights in Beijing?

Answer 1

Solution 1(map)

If you have a map of beijing you can count the roads from south to north and east to west. By 2013 there are 30 in both directions (Beijing is basically a circle).

30 x 30 makes about 900 intersections. Each intersection has 4 traffic lights so the total number would be 3600. For a more precise result you must also count in each T and dead end road.

Solution 2(map)

A little faster is it if you take the city as a circle and go from the middle to the outskirts in a view straight lines. Count all numbers together devide it by the number of probes you got x 360 and you should also get a reliable result. But you need to take the right lines and right amount of lines in the most and the least populated areas to become reliable numbers. I come to the middle measure of 2,6 which equals 3888 red lights

Solution 3(Demographics)

This solution is based on data you can find online. I could not find any up to date numbers so I had to calculate.

The idea is that the number of traffic lights is raising equal to the total population count.

Beijing grew by about 600000 people every year between 2000 and 2010.

From the Beijing Goverment Hompage we find that in 2007 the there were 2747 traffic lights. Based on the wiki data we can estimate the population for 2007 to about 17,2 mio and 2013 about 21,4 mio, therefor there should be about 3417 traffic lights by now.

A more precise result would be possible by taking the population growth as an exponential graph.

It means also that there are 6261 people for one red light. We could compare this number with other cities and find so a more general Hypothesis for the correlation between red lights and people in chinese cities.

Solution 4(Sales)

In a hypothetical situation you could call manufacturers of traffic lights for market data. Probably you could also try to call the traffic section or the munincipal goverment itself.