What time period? The standard lane width has been 12' since at least the 60's. As late as the late 40's it was 9'. What locale? The above is for highway construction. Cities often cheat, even today, with lanes of 11' and sometimes even 10'. An example being that street might be built for 4 lanes thus 12' times 4 for 48'. Later developement dictates that a left turn lane is needed and instead of widening the street to 60', a city will just restripe the 48' street into 5 lanes with the left turn lane 8' wide.
As Larry says, cities just tend to fake it, even though there are standards. Also realise that at a scale of 167:1, being a foot or 2 out probably isnt going to make an earth shattering difference, visually. Aim at 10' lane width and if you err slightly to either side you'll be fine. a 10' lane, fyi, is 7/10th of an inch.... so 1.5" should look pretty good for 2 lanes.
