You are looking at an OO Gauge Double Twin Stonework Railway Train Tunnel Track Double Portal Entrance - so should be good for 4 tracks.
Portal dimensions are added as an extra image but basic dimensions in text format below, keep in mind when looking at the image there are 2 of these in this set and the dimensions do not include the side wall sections.
Portal size x 2: 16.2cm W x 0.79cm D x 11.6cm H
Edge caps joining piece: 1.9cm W x 1.0cm D x 12.5cm H
Total width when set up as per image 1: 35.5cm
Please Note: These items are 3d printed, far more sturdy than plaster or laser cut cardboard models, all items come unpainted in grey.