The most common vehicle used by the Royal Engineers in road construction/repair was the Foden Steam Wagon. There is one original and complete one at Kew (London).
Hopefully you should be able to access a picture of it here:
Hi GWT, Thanks for the pic I already have this though.. there is another thread on the forum dealing with Fodens to some extent where you will find another pic of a restored Foden that was said to have had War service.....
OK. Thanks for the link there. This forum has attracted some very knowledgable people. My understanding is, that apart from the steam wagons, all sorts of soft skin trucks were used, but it was not uncommon to see them marked as this Kelly Springfield below.
I presume that markings such as these gave them an element of priority on busy or restricted roads.
As Tim says, all sorts of lorries were used for road work. ASC Companies seem to have been rotated, the same as the men in the trenches were, so they would spend time on the front line, then move back to spend time on roads, then further back for general duties, rest and repairs. Therefore most ASC Companies were involved on road work for periods and the lorries used would have been whatever was in any particular company at the time. 50 coy ASC had some lorries repainted dark red so they were easily noticed and given priority over other traffic, though I don't know what make they were. 50 Coy had a mix of Dennis, Maudslay, Commer, Napier and Wolseley when in France, though also had Karrier, Albion Leyland and Lacre when in Ireland and on the Home Front.