Here's a map of the proposed downtown Durham section of the Durham-Orange light rail route:  

The longer tunnel will be approximately a third of a mile in length.

Here's a side view map:

Some preliminary cost estimates:

• $10 million for the Duke Street underpass
• $55 million for tunnel at Blackwell and Mangum streets
• $12 million for bridge at Dillard and Fayetteville streets
• $3 million for Grant Street connectivity improvements
• $8 million for design costs

Source: GoTriangle

Concerns

Costs for the DOLRT have exploded.  The aforementioned tunnels have only recently (4Q2018) been proposed, and the preliminary cost estimates are likely well below their actual costs.  Where will the money come from?  In my opinion, money will have to moved from other budget line items ... like schools, greenways, buses, and affordable housing ... or, taxes will have to be raised significantly. 

The tunnels were proposed, because downtown business owners finally woke up and realized all the traffic turmoil that DOLRT's at-grade crossings would have on their business district. 

In my opinion, DOLRT should be scuttled.  [details]