But Murdock was too useful a man to Boulton & Watt to be allowed to have free rein, and his inclination toward steam locomotion invention was apparently curbed, though it would appear Watt thought the roads of that time an insurmountable obstacle to the development of road vehicles, and wanted Murdock to devote his time to mechanical matters more ripe for success. Boulton, writing to Watt from Truro, in September, 1796, tells how he met Murdock on his way to London to get a patent on a new model, and how he persuaded him to turn back. This model was for a steam carriage that was afterward shown as able to travel freely around a room with a light load of shovel, poker and tongs upon it. His was probably the first high-pressure steam-engine vehicle run in England. Though only a small model, it did its proportionate work well.
Watt continued to oppose Murdock's scheme, but on one occasion suggested that he should be allowed an advance of five hundred dollars to enable him to prosecute his experiments, and if he succeeded within a year in making an engine capable of drawing a post chaise, carrying two passengers and the driver, at four miles an hour, it was suggested that he should be taken as partner into the locomotive business, for which Boulton and Watt were to provide the necessary capital. This proposition was never carried out. Again, in 1786, Watt said: "I wish William could be brought to do as we do, to mind the business in hand, and let such as Symington and Sadler throw away their time and money in hunting shadows." Murdock continued to speculate about steam locomotion on common roads, but never carried his ideas further. He retired from the employment of Boulton & Watt in 1830, and practically retired from all work at the same time.
Murdock seems to have had a very clear idea of the possibilities of steam propulsion on the common roads. Had circumstances permitted he might well have been expected to have solved the problem in 1796 quite as completely as his successors did in 1835. But he was a quarter of a century ahead of the time. Even the moderate public interest that existed later on had not manifested itself at all in his day and the condition of the English highways offered almost insuperable obstacles to steam vehicular travel. Personally his lack of self-assertiveness and his feeling of dependence upon Boulton and Watt also held him back. So he remained simply one of the pioneer investigators pointing the way for others.