Accessing it is just a matter of bringing up the directions feature on Google Maps, this time when you enter in your locations, alongside the estimated time it takes to travel from point A to B, there will be an estimate underneath it that factors in current traffic conditions. The information offered is regularly updated so that you can adjust your travel plans in due course.
The idea is that through this feature, you can estimate how long it will take to travel using different modes of transport and find the quickest method. So comparing driving to public transport or cycling may show that the latter option is the fastest if faced with current traffic conditions.
Google say that it’s available in specific areas for now, mainly in U.S. cities, but like all Google products, it’s only a matter of time before the service is expanded to other countries.