The utility model discloses a crossroad shows optimum speed's intelligent transportation system, include: traffic road conditions monitoring module, vehicle speed measuring module, data storage and sharing module, optimum speed calculation module and optimum speed display module, optimum speed calculation module depends on traffic road conditions monitoring module and vehicle speed measuring module, traffic road conditions monitoring module and vehicle speed measuring module offer optimum speed calculation module with data, it is next through showing that screen display demonstrates that the optimum speed display module calculates the data that reach to optimum speed calculation module, inform that suggestion speed that the driver calculated according to the system needs the car and travel, thereby avoid in the at utmost meetting the red light at next crossing, shorten the time of vehicle through the red light on the one hand, save driver's time, on the other hand is the problem from alleviating the traffic jam to a certain extent also, improve the utilization ratio of road. This intelligent transportation system has intellectuality and hommization concurrently, has extensive development space in the transportation systems in future.