For an Operational Analysis of a traffic signal approach, one 11-foot-wide through lane on a 2% downhill grade has neither left turning nor right turning traffic. The change and clearance interval (yellow plus all-red) is 4.0 seconds. The percentage of heavy vehicles is 2%. Parking is prohibited and there are no bus stops. If the signal is located in a Central Business District, determine the saturation flow rate for the 11-foot lane under prevailing conditions, in vehicles per hour.