Time-Dependent Contraction Hierarchies and Approximation

Time-dependent Contraction Hierarchies provide fast and exact route planning for time-dependent large scale road networks but need lots of space. We solve this problem by the careful use of approximations of piecewise linear functions. This way we need about an order of magnitude less space while preserving exactness and accepting only a little slow down. Moreover, we use these approximations to compute an exact travel time profile for an entire day very efficiently. In a German road network, e.g., we compute exact time-dependent routes in less than 2 ms. Exact travel time profiles need about 33 ms and about 3 ms suffice for an inexact travel time profile that is just 1 % away from the exact result. In particular, time-dependent routing and travel time profiles are now within easy reach of web servers with massive request traffic.