Here's a picture of the TexRail route to Terminal B.
https://ridetrinitymetro.org/wp-content/uploads/2018/09/Map-2016-7.png
From FAQs:
There are two main reasons why TEXRail will use diesel technology. The cost (both construction, and ongoing operational costs) of an electrified rail system is much higher than a diesel rail system, and the existing railroad tracks on which TEXRail will share with freight railroads do not have electrification.
The speed of train travel will depend on the type of terrain, the number of crossings, the current train location on the line and other related factors. Speeds likely would range from 0 to 70 mph.
Trinity Metro is working with existing railroads to share existing tracks, which would mean most of the route would operate on a single track. Selected locations will have a second track added for passing ability, and to meet schedules for both passenger and freight traffic. Double tracks also will be placed at stations.
The train frequency projected is for the year 2035. Projections for population, employment growth and other factors would be needed to project any increase in train frequency beyond 2035.
During peak hours, (the three hours associated with morning rush hours, and the three hours in the evening associated with evening rush hours), trains will run about every 30 minutes. Outside of peak hours, trains would run about every 60 minutes. This frequency is expected to occur in the year 2035, with less frequency possible at startup. Train service and frequency would be consistent along the entire length of the route.
TEXRail DFW International Airport Station will be connected to DART Orange Line DFW International Airport Station via a short walk. (Time of this short walk is not stated.)
The railroads that own the current train bridge crossings over the Trinity River have indicated those bridges are or will soon be at capacity, and there would be no opportunities for the proposed passenger trains to get across using the existing bridges. The railroads also have indicated concerns about liability issues related to allowing a passenger train to use their bridge crossings.