A block signal uses colored lights to inform a train engineer of the traffic condition in the next track block. A green light indicates that the block ahead is clear; a red light indicates the next block is occupied.

The Lionel 153 Automatic Block Signal has been available, almost continuously, since 1940. It is still available from Lionel and Mike's Train House has an accurate reproduction.

It is 9" high, making it a 1:48 scale model of a 36' high railroad signal. While a bit tall for O Gauge, it serves well for a toy train layout: the lights are bright and are easily noticed.

The light green base and black lights fixture are diecast metal. The post, finial cap, orange ladder, and ladder bracket are formed sheet metal. Some modern versions have a black base.

Pre-1950 versions of the 153 used screw-base 6-8 volt bulbs (L50R and L50G) and a resistor (in the base) so the 153 could be operated from track power. (Click the number for bulb specifications.)

After 1950 and modern versions use 14-volt bayonet bulbs ( L53R and L53G , 14 volts, but listed as 12-16 volts).

Note that track power can be more than 14 volts; if bulbs are burning out too quickly, consider using a separate 12-14 volt transformer connection, rather than track power, for the accessory or change to 1445 bulbs.

Electrical connections for the 153 Block Signal are made to three terminal posts on the base. The center post is common to both lights and is usually connected to one side of a 12 volt accessory transformer. The other two posts connect to one of the light bulbs, as shown in the diagram. The light bulb connections are wired to the device for controlling the signal.

A 153C double-throw weighted contactor was, and still is, packed with the 153. Lionel's advertising copy for the 153 suggested the accessory actually controlled two trains on the same track, but it never has.

The 153 can also be operated with two insulated-rail track segments. Make two isolated outside rail track blocks, say three feet long or more, and connect each to one light. With appropriate transformer connections, the light will be on when a train is in the connected track block. Not exactly prototypical, but the changing lights add a little action to the layout.

And, of course, the 153 Block Signal can be operated with Three- Rail Innovations' Universal Trackside Accessory Controller . The UTAC has six configurations (in each bank) for operating one or two 153 Block Signals. Thus, one to four block signals can be operated by one UTAC.

The following diagram shows the general wiring for connecting a 153 to the UTAC. Select appropriate input and output connections for the configuration used.

Two block signals can also be connected to the same UTAC outputs. Say they face opposite directions of the same track block to show block conditions for trains coming in each direction. Different trackside accessories at each end of the track block can also be activated with the same UTAC outputs. For example, semaphores used in a series of blocks in one direction, and block signals for the other direction.

Operation does not have to be prototypical. A block signal has two lights and the UTAC can be connected to operate the lights anyway you want. Some examples: configuration 6 or 13 to flash one light; configurations 7 - 12 to alternately flash the lights (or just one light, only make one connection and use the other for something else); configuration 14 to flash a light at a rapid rate.

It's your railroad, you can make the block signal lights do anything you want.

The Two Relay Controller has four features for operating block signals: Off/On, Prototypical, Flashing, and Warning. Click on any of the following for examples.