Can transit projects be judged based on the "welfare" of various user groups?

If you know how to equate the "welfare" of a transit rider with the "welfare" of a motorist, and are not concerned with any other forms of welfare, you can do a calculation that appears to say whether a transit project was a good idea.

From a new paper in World Transit Research by Rémy Prud'homme.

In Paris, an old bus line on the Maréchaux Boulevards has been replaced by a modern tramway [the T3, opened in December 2006]. Simultaneously, the road-space has been narrowed by about a third. A survey of 1000 users of the tramway shows that the tramway hardly generated any shift from private cars towards public transit mode. However, it did generate important intra-mode [shifts]: from bus and subway towards tramway, and from Maréchaux boulevards towards the Périphérique (the Paris ring road) for cars. … The welfare gains made by public transport users are more than compensated by the time losses of the motorists, and in particular, by the additional cost of road congestion on the Périphérique. The same conclusion applies with regard to CO 2 emissions: the reductions caused by the replacement of buses and the elimination of a few cars trips are less important than the increased pollution caused by the lengthening of the automobile trips and increased congestion on the ring road. Even if one ignores the initial investment of 350 M€, the social impact of the project, as measured by its net present value is negative. This is especially true for suburbanites. The inhabitants (and electors) of Paris pocket the main part of the benefits while supporting a fraction of the costs.

So here is our plate of facts:

On series of boulevards running parallel to the Périphérique, the motorway that circles Paris, traffic lanes were removed and a light rail line was added. This was done less than five years ago.

The light rail line didn't attract new riders beyond those already on the bus and subway systems.

The closure of traffic lanes caused traffic to shift from the boulevards to the motorway, increasing congestion on the motorway, therefore affecting many motorists traveling long distances around the edges of the city. .

As a result, the benefits tended to fall heavily within Paris, among public transit patrons on affected boulevards, while the disbenefits fell on suburban motorists.

All that may be true. Does this mean the rail line was a mistake? Discuss.