Keep taking the commuter rail, or start driving? As commuters absorbed news of a proposal to substantially hike fares on commuter lines - for some, a year’s worth of fares would approach $4,000 - some began doing the math to figure out whether it would be cheaper to drive. And that’s exactly what some rail commuters are planning to do, in the wake of an MBTA proposal that would hike the cost of a monthly pass $11 to $64.