TP&T has conducted over 600 speed studies since 1987. Some locations have been studied more than once. The speed of each passing vehicle is recorded by radar for an hour each in the morning rush hour, evening rush hour, an midday. (Like many things in nature, the speeds we record on Cambridge streets follow a normal distribution.) From these results, we find the 85th percentile (%ile) speed for each one-hour period. The 85th percentile speed describes a speed that 85% of drivers are traveling slower than (and 15% of people are driving faster than). Traffic engineers use 85th percentile speed for most traffic safety analyses and design standards.
In the chart below, the speed reported is the highest 85th percentile speed for all three one-hour periods studied. For more about posted (and unposted) speed limits and how fast is too fast, please see our main speeding page.
Pan and zoom around the map to explore Speed Study locations around Cambridge. You can also type in an address to find Speed Studies on a specific street.