As road closures for this weekend’s Indy race snarl traffic around Exhibition Place, a new report says the true cost of gridlock in Toronto may be far higher than current estimates.

It has long been reported that traffic congestion costs the Greater Toronto and Hamilton Area about six billion dollars a year. But the C.D. Howe institute says that figure doesn’t take into account the social costs of gridlock.

The institute says clogged traffic can cause skilled workers and others not to move to Toronto, and reduces demand for more business, entertainment, and cultural opportunities.

When those losses are factored in, the cost of gridlock could almost double to $11-billion a year.

The C.D. Howe institute says governments need to develop a more accurate model for estimating the costs of traffic congestion, so that they can make more informed decisions about where to invest in infrastructure improvements.