Average progress on the tunnels was 8 feet per day (0.028 m/ks).
The aggregate length of the five tunnels is 9,947 feet (3,032 m) as completed (10,180 feet (3,100 m) as designed), which is one-fifth of the entire 9.81-mile (15.79 km) length of the Bayshore Cutoff.
Each tunnel shares the same cross-section design, being a semicircular arch 30 feet (9.1 m) wide to accommodate two tracks spaced 13 feet (4.0 m) apart (centerline to centerline).
Overall height in the center of the tunnel is 27 feet (8.2 m), with clearance of 22 feet (6.7 m) above the top of the rail at each track centerline.
The tracks are elevated 1 foot 8 inches (0.51 m) above the tunnel floor by ballast and ties.

Tunnel 2 was built using cut-and-cover, but the other four were built by first sinking pilot drifts approximately 8 by 7 feet (2.4 by 2.1 m) in cross-section at the bottom corners of the tunnel.
After these first two drifts were completed, the concrete side walls were partially built and timber supports were placed to allow the excavation of two more drifts on top of the first drifts up to the springing line where the semicircular brick arch meets the concrete side walls.
With the side drift excavation complete, the concrete side walls are poured.
A fifth drift was then bored at the apex of the tunnel, followed by excavation of the remaining space between the apex and side drifts.
Once these initial excavations were complete, leaving a "core" of rock in the center of the tunnel, timber bracing was placed to support the rock at the top of the tunnel and a steel arch form was installed.
After covering the arch form with planks, five to six layers of brick were laid to form the semicircular arch, resting on concrete side walls.
The space between the top of the arch and the excavated tunnel was backfilled with loose rock, or concrete if the pressure was especially large.
The temporary timber supports and arch form were removed, and the remainder of the tunnel was cleared by blasting, with the blasted rock being sorted for incorporation in the concrete.

Tunnels 1 and 2 bracket the present-day 22nd Street station.
Tunnel 1 is just north of the station, and Tunnel 2 is south.
Both tunnels are cut through Potrero Hill.
Tunnel 2 is the only one of the five tunnels built with twin bores to accommodate four tracks, although the western bore is currently closed.
The western bore was built because a high concrete retaining wall was needed to support a city street running alongside that second tunnel.
Tunnel Top Park, at 1100 Pennsylvania Avenue, is within the Caltrain-owned right-of-way.
These two tunnels were bored through mostly serpentinite rock with clay seams.

The Western Pacific Railroad (WP) also built a tunnel through Potrero Hill at nearly the same time; support timbers within the Western Pacific tunnel caught fire in 1962, leading to its collapse and subsequent fill.
The area on top of the WP tunnel remained undeveloped until the 1990s.

Tunnel 3 traverses the Hunters Point neighborhood.
It was built under the St. Joseph's orphan asylum.
The tracks are 175 feet (53 m) below the ground's surface.
Tunnel 3 is bored through wet sand and hard silicated formations.

Tunnel 4 crosses Candlestick Point.
The former Schlage factory and headquarters, constructed in 1926, are located just west of the southern portal of Tunnel 4.
In 1907, it was noted that Tunnel 4 had been bored through very wet ground and partly through shale.
The earthquake of April 1906 caused a spring to start leaking into Tunnel 4, which went unnoticed until several months after the seismic event, when the reinforced concrete of the completed tunnel began to bulge, eventually causing water to leak into the tunnel.
The spring was not capped until 1911.

Tunnel 5 crosses Sierra Point and was bored through hard sandstone.
Tunnel 5 was abandoned in 1956 when the old Bayshore Highway (which is now the present-day Bayshore Boulevard in Brisbane and South San Francisco) was expanded into the six-lane divided Bayshore Freeway.
The route for the freeway was moved to the east along a new causeway const
Average progress on the tunnels was 8 feet per day (0.028 m/ks). The aggregate length of the five tunnels is 9,947 feet (3,032 m) as completed (10,180 feet (3,100 m) as designed), which is one-fifth of the entire 9.81-mile (15.79 km) length of the Bayshore Cutoff. Each tunnel shares the same cross-section design, being a semicircular arch 30 feet (9.1 m) wide to accommodate two tracks spaced 13 feet (4.0 m) apart (centerline to centerline). Overall height in the center of the tunnel is 27 feet (8.2 m), with clearance of 22 feet (6.7 m) above the top of the rail at each track centerline. The tracks are elevated 1 foot 8 inches (0.51 m) above the tunnel floor by ballast and ties.
Tunnel 2 was built using cut-and-cover, but the other four were built by first sinking pilot drifts approximately 8 by 7 feet (2.4 by 2.1 m) in cross-section at the bottom corners of the tunnel. After these first two drifts were completed, the concrete side walls were partially built and timber supports were placed to allow the excavation of two more drifts on top of the first drifts up to the springing line where the semicircular brick arch meets the concrete side walls. With the side drift excavation complete, the concrete side walls are poured. A fifth drift was then bored at the apex of the tunnel, followed by excavation of the remaining space between the apex and side drifts. Once these initial excavations were complete, leaving a "core" of rock in the center of the tunnel, timber bracing was placed to support the rock at the top of the tunnel and a steel arch form was installed. After covering the arch form with planks, five to six layers of brick were laid to form the semicircular arch, resting on concrete side walls. The space between the top of the arch and the excavated tunnel was backfilled with loose rock, or concrete if the pressure was especially large. The temporary timber supports and arch form were removed, and the remainder of the tunnel was cleared by blasting, with the blasted rock being sorted for incorporation in the concrete.
Tunnels 1 and 2 bracket the present-day 22nd Street station. Tunnel 1 is just north of the station, and Tunnel 2 is south. Both tunnels are cut through Potrero Hill. Tunnel 2 is the only one of the five tunnels built with twin bores to accommodate four tracks, although the western bore is currently closed. The western bore was built because a high concrete retaining wall was needed to support a city street running alongside that second tunnel. Tunnel Top Park, at 1100 Pennsylvania Avenue, is within the Caltrain-owned right-of-way. These two tunnels were bored through mostly serpentinite rock with clay seams.
The Western Pacific Railroad (WP) also built a tunnel through Potrero Hill at nearly the same time; support timbers within the Western Pacific tunnel caught fire in 1962, leading to its collapse and subsequent fill. The area on top of the WP tunnel remained undeveloped until the 1990s.
Tunnel 3 traverses the Hunters Point neighborhood. It was built under the St. Joseph's orphan asylum. The tracks are 175 feet (53 m) below the ground's surface. Tunnel 3 is bored through wet sand and hard silicated formations.
Tunnel 4 crosses Candlestick Point. The former Schlage factory and headquarters, constructed in 1926, are located just west of the southern portal of Tunnel 4. In 1907, it was noted that Tunnel 4 had been bored through very wet ground and partly through shale. The earthquake of April 1906 caused a spring to start leaking into Tunnel 4, which went unnoticed until several months after the seismic event, when the reinforced concrete of the completed tunnel began to bulge, eventually causing water to leak into the tunnel. The spring was not capped until 1911.
Tunnel 5 crosses Sierra Point and was bored through hard sandstone. Tunnel 5 was abandoned in 1956 when the old Bayshore Highway (which is now the present-day Bayshore Boulevard in Brisbane and South San Francisco) was expanded into the six-lane divided Bayshore Freeway. The route for the freeway was moved to the east along a new causeway const
Bayshore Cutoff