As Chief Engineer at Mont Blanc; Polonceau worked on the Simplon, Lautaret and Mont-Cenis Alpine roads between 1808 and 1812. He then became interested in factories, peat bogs and waterways as director of waterways in the Département of Seine-et-Oise and the Seine navigation department.
But Polonceau distinguished himself by his ingenuity in many other areas too.
He introduced the macadam pavement to France and recommended use of road rollers to improve stone roads.
He is cheifly remembered today for his original and inexpensive innovations for cast-iron bridges, aiming for uniform elasticity and light components in preference to the heavy rigid structures then in vogue. After the small three-arch bridge he designed in 1822 at Maisons near Paris, he applied his patents to the construction of iron and cast iron bridges for a Parisian contractor.
The Pont du Carrousel, built between 1831 and 1834, is the perfect illustration of his thoeries and shows that a bridge can withstand heavy loads while using much less cast iron than Southwark bridge, for example. Hollow cast iron arches mean the structure is light, solid and economical, as Polonceau described in a paper published in 1839.
After 1830, he was engaged in design work for several railway lines, including the Paris-Orléans, Orléans-Bordeaux and Paris-Rouen lines, and as far as Le Havre and Dieppe along the Seine valley, the route which was to be chosen later.
His large number of publications and technical notes also bear witness to his immense curiosity in a large number of topics, including hailstones of unusual shapes and sizes, kashmir goats, the drainage and cultivation of forests, bitumen and its various uses, the harvesting of hay, improving the regimen of the river Yvette and the operation of the Grignon School of Agriculture (which he founded in 1827), the use of water in agriculture, windmills and even Swiss cows!
Later in life he became profoundly deaf and retired to the Franche-Comté region where he spent most of his time working on agricultural improvements.