Maceroni was second only to Walter Hancock as an inventor and builder of steam road carriages and as a promoter of travel by those vehicles. From 1825 to 1828 he was with Goldsworthy Gurney in London, but his real activity did not begin until 1831, when he became associated with John Squire. In 1833, Maceroni and Squire took out a patent for a multi-tubular boiler, which they applied to a steam carriage that one writer of that day described as "a fine specimen of indomitable perseverance." It often traveled at the rate of from eighteen to twenty miles an hour. The engines were placed horizontally underneath the carriage body, the boiler was arranged at the back, and a fan was used to urge the combustion of the fuel, the supply of which was regulated by the engineman, who had a seat behind. The passengers were placed in the open carriage body, and their seats were upon the tops of the water tanks. There were two cylinders seven and one-half inches in diameter, the stroke being fifteen and three-quarter inches. The diameter of the steam pipe was two and one-quarter inches, and that of the exhaust pipe was two and three-quarter inches. The carriage attracted a great deal of attention, and much was written about it in the newspapers of the time. Once the trip was taken to Harrow-on-the-Hill, a distance of nine miles, in fifty-eight minutes, without the full power of steam being on at any time. For several weeks in the early part of 1834 the carriage was running daily from Oxford Street to Edgeware. Several trips were made to Uxbridge, when the roads were in very bad condition, but the journey from the Regent's Circus, Oxford Street, a distance of sixteen miles, was often performed in a little over an hour. A trip to Watford was made, and one of the passengers thus described the experience from Bushby Heath into the village of Watford: "We set off from the starting place amid the cheers of the villagers. The motion was so steady that we could have read with ease, and the noise was no worse than that produced by a common vehicle. On arriving at the summit of Clay Hill, the local and inexperienced attendant neglected to clog the wheel until it became impossible. We went thundering down the hill at the rate of thirty miles an hour. Mr. Squire was steersman, and never lost his presence of mind. It may be conceived what amazement a thing of this kind, flashing through the village of Bushy, occasioned among the inhabitants. The people seemed petrified on seeing a carriage without horses. In the busy and populous town of Watford the sensation was similar--the men gazed in speechless wonder; the women clapped their hands. We turned round at the end of the street in magnificent style, and ascended Clay Hill at the same rate as the stage coaches drawn by five horses."