Contact duration between moving vehicles is a key metric that influences routing schemes and network throughput in vehicular ad hoc networks (VANETs). An analysis of contact records from tens of thousands of taxis in Beijing found that contact duration exhibits an exponential distribution for at least 80% of the distribution, up to a characteristic time point, after which it follows a power law distribution. This contrasts with human mobility studies where contact duration shows a pure power law distribution. These findings provide guidance for designing new routing protocols for urban VANETs.