He's more referring to where Commuter Rail, not subway, is the method. Problems notwithstanding, subway lines other than the Green Line will always win over driving during peak times.

A great example would be coming from Waltham via the Worcester/Framingham Line versus driving along the Mass Pike -- it'd be a coin flip as to what wins on a given day.

Moreover, outside of subway service the only alternative (where available) is bus which can easily double commute times compared to driving. In some cases (Waltham and Newton for example) there's the Inner/Outer Express Buses which also competes directly with Commuter Rail in terms of timeliness (10% slower on average) but at a lower cost -- you can take non-express buses as well which are cheaper still, but tack on another 35-45 minutes each way -- we're talking 3 to 4 hours of commuting a day from northern parts of Boston to central Waltham via a combination of subway and non-express buses.

However, Commuter Rail tends to be faster than driving on longer trips. Such as coming from Providence, Worcester, Fitchburg, etc.