On-board emissions measurement for heavy-duty vehicles has taken on greater significance because new standards now address in-use emissions levels in the USA. Emissions compliance must be shown in a “Not-to-exceed” (NTE) zone that excludes engine operation at low power. An over-the-road 1996 Peterbilt tractor was instrumented with the West Virginia University Mobile Emissions Measurement System (MEMS). The researchers determined how often the truck entered the NTE, and the emissions from the vehicle, as it was driven over different routes and at different test weights (20,740 lb, 34,640 lb, 61,520 lb, and 79,700 lb) The MEMS interfaced with the truck ECU, while also measuring exhaust flowrate, and concentrations of carbon dioxide (CO2) and oxides of nitrogen (NOx) in the exhaust. The four test routes that were employed included varying terrain types in order to simulate a wide range of on-road driving conditions. One route (called the Bruceton route) included a sustained hill climb. Another route (known as the Saltwell route) traversed more rolling hills throughout the duration of the test. For 34,640 lb and 79,700 lb, the vehicle was tested on a route that was a reasonably flat road (PA 43 route), and a route through city traffic (Stop-n-go). As an example of results from the study, on the Bruceton route at 20,740 lb, the truck spent only 8.24% of the time within the NTE, but at 80,000lb on the same route it spent 35.67% of test duration in the NTE. Distance-specific NOx and fuel consumption were typically 50 to 80% higher in the NTE zone than over the whole route.