On 3 November 2007, the Sichuan Transportation Bureau announced that the Sui-Yu Expressway was completed after three years of construction. After completion of the Chongqing section of the road, the 36.64 km (22.77 mi) expressway connected Cheng-Nan Expressway and formed the shortest expressway from Chengdu to Chongqing. The new expressway is 50 km (31 mi) shorter than the pre-existing road between Chengdu and Chongqing; thus journey time between the two cities was reduced by an hour, now taking two and a half hours. The Sui-Yu Expressway is a four lane overpass with a speed limit of 80 km/h (50 mph). The total investment was 1.045 billion yuan.

Answer this question, if possible (if impossible, reply "unanswerable"): What is the speed limit on the Chengdu expressway?
unanswerable