I don't think Google will provide this API. And traffic data not only contains the incident data.
Today many online maps show city traffic, but they have not provide the API for the developer. We even don't know where they get the traffic data. Maybe the government has the data.
So I think you could think about it from another direction. For example, there are many social network website out there. Everybody could post the traffic information on the website. We can collection these information to get the traffic status. Or maybe we can create a this type website.
But that type traffic data (talked about above) is not accurate. Even the information provided by human will be wrong.
Luckily I found that my city now provides an Mobile App called "Real-time Bus Information". It could tell the citizen where the bus is now, and when will arrive at the bus station. And I sniff the REST API in this App. The data from REST API give the important data, for example the lat and lon, and also the bus speed. And it's real-time data! So I think we could compute the traffic status from these data (by some programming). Here is some sample data : https://github.com/sp-chenyang/bus/blob/master/sample_data/bjgj_aibang_com_8899_bjgj_php_city_linename_stationno_datatype_type.json
Even the bus data will not enough to compute the accurate real-time traffic status. Incidents, traffic light and other things will affect the traffic status. But I think this is the beginning.
At the end, I think you could try to find whether your city provides these data.
PS: I am always thinking that life will be better for people in the future , but not now.