Verified answer

It's not really a market failure. It's government creating a system that truncates market behavior. On unmetered roads the marginal cost of traveling on it is essentially zero. While the value of getting from point A to point B in time T differs among the travelers, the cost of doing so is the same for all. Ergo limited space/time is allocated inefficiently. Metered roads avoid this issue by charging fees that eliminate low value traffic that doesn't value time enough to pay the toll.