"road system" is correct and usable in written English.
You can use it to refer to a network of roads. For example, "The city has an extensive and well-maintained road system."
The state's road system is limited.
Mudslides have damaged the precarious road system.
In earlier interviews, some protesters said they hoped to paralyze the road system in downtown Vancouver.
That the American road system is a crowning achievement of Western civilization is too little appreciated.
In Rome the road system began from the Golden Milestone in the Roman Forum.
The road system is well developed and in good repair, and almost all roadways are paved.
Like the railways, the road system is radial in design, with Madrid as its hub.
An inadequate road system leading to the various terminals also continues to hamper growth.
It has 670,000 inhabitants, poor public health and a broken and clogged road system.
The road system remained extremely inadequate, as was demonstrated in the Crimean War.
Bournemouth has a strange road system that involves two separate streets having the same name.
