BELOW STREET LEVEL
Out on the street along their routes, the cable cars travel on steel tracks set above a channel enclosing the cable. At the top of the channel is a slot through which the
Cable Car’s grip grabs the cable moving below. This distinctive feature of cable railway gave its name to a large district south of Market Street, the large business thoroughfare running on a diagonal southwest from the Ferry Building on the Embarcadero to Twin Peaks. Early cable car lines competed for space down the center of the street, and everything to the south of this was referred to by locals as "south of the slot", a nickname that lives on with longtime San Franciscans.
The track structure not only supports the tracks themselves, but also the cable and the cars. This is accomplished through a series of yokes, spaced at intervals along the track, and made of steel set in concrete; formerly paving stones were set at street level between the tracks and slot, again after 1982 concrete casing was used exclusively. Carrier pulleys spaced every fifteen feet support the wire rope in the channel. Original channels along the Clay Street Hill Railroad were constructed of redwood planking and cast iron yokes to keep the building costs to a minimum. Later extensions and new cable companies utilized concrete and heavier iron yokes to strengthen and extend the life of the channels.
Other pulleys are a bit more complicated in design and function. Depression bar pulleys are used to keep the cable down at the bottom of a hill; otherwise it would rise out of the slot. This necessitates placing the pulleys on top of the cable, but then the grip encounters interference as it tries to pass. To solve this, the depression pulleys are connected to a depression bar which pivots aside as the pulleys are freed by the passing grip, then swivels back into place after the car has passed. Access to this bar, like the carrier pulleys, is through a large steel plate in the street.
Another type is known as the stationary depression pulley. This arrangement requires the cable car gripman to release the cable from the grip as it passes over. Steel plates or bright yellow lettering painted on the street warn the gripman to "Let Go". Letting go of the cable is necessary when two cables intersect at a crossing, the car passes a particular type of turn called a let-go curve, or when the gripman must release one cable and pick up another. If the gripman did not "let go", then substantial damage would be done to the cables and grip itself.
To keep this from happening, these points have a bumper bar and bell feature to ensure safety and prevent damage to the system. If the grip is not "dropped" at the Let Go notice, then the cable will raise the bumper bar, dropping counterweights, and turning the pulley against the cable, which rings an alarm bell to alert the errant gripman to drop the cable. If for some reason the cable is still not dropped, then the bumper bar forces the cable out of the grip, causing damage however to both grip and cable, but preventing more serious and extensive damage to the system. The powerhouse is then notified of the incident and inspects for damage to the cable.
While snapped cables are very rare, the occasion broken strands do occur. In this situation the cable must be fixed immediately, because a broken strand caught in the grip has been the cause of accidents in the past.
Once the car has cleared the let-go, the gripman must pick up the cable again. After the let-go point, there is a dip in the tracks, which enables the grip to grab the cable without stopping. Another method is to use the cable lift level, at terminals or areas where the track dip is not available. The car operator lifts up the level and the pulley in the slot raises the cable into the grip. When some cars employed a side-grip however, then a lift rod was raised using a chain, causing the cable to slide down into the side of the grip. This arrangement is called a "gypsy chain" and is operated by the conductor after the car crosses the intersection. The last company to use a side grip was the California Street Cable Railroad, and after the Municipal Railway acquired it in the 1950s, the grips were changed to the now universal bottom grip used by the other lines.
Then in 1883, the Sutter Street Railroad introduced pull curves, invented by George Duncan for the Dunedin & Roslyn Tramway Company of Dunedin, New Zealand. This type of curve could be installed at any intersection, regardless of street physiognomy. The pull curve involved a series of many small pulleys holding the cable in place as it makes the turn. When the car approaches, the grip is pushed away from the pulleys and guided by a chafing bar set above and outside the pulleys, negotiates the turn. After the turn is completed, the cable returns to its usual position on the pulleys.
This type of curve is recognizable by the series of access plates abutting one another around a turn. All of these turns have given rise to the colorful shout of the conductor: "Look out for the curve", often parodied by writers as a brassy Brooklyn dialect, although it is more likely to have been a Mission district accent at the time, similar in tone, yet distinct and almost extinct in modern San Francisco.
Finally, the cable car system employs two types of terminal arrangements for sending cars back up their route. The California line uses a double-ended "California Car" with identical machinery on either end, except for the grip, which fastens to the opposite lever by a connecting rod. This allows the car to proceed back on its route from either terminal without turning the car physically around. Instead the car uses a system of switchbacks and crossovers on the tracks to set up the cars for a return trip. This arrangement was used on early cable car lines, like the Clay Street Hill Railway, to facilitate changing direction. The California Street Cable Railroad used this on the California street line and continues to do so to this day.
The so-called combination car used on the Powell and Mason lines has only one set of levers and grip, and so this necessitates use of a turntable. The gripman lets-go the cable and the car coasts onto the turntable. It is then turned around by manpower, much as it has since the 19th century. In early days and up until the 1970s, many in the crowd at the terminal assisted in helping the conductor and gripman in the process getting the best seats before the others waiting at the stop. This practice was discontinued and now crowds wait orderly in line while the conductor and gripman work alone.