GWR Power and Weight Classification

Erlestoke Manor was rated axle load class ‘Blue’ and power class D

On 1 July 1905 the GWR introduced a system for denoting the haulage capabilities and weight restrictions applicable to the various classes of their locomotives. From mid-1919 this information began to be displayed on the locomotives themselves, enabling railway staff to make a quick assessment of a locomotive's capabilities without the need to refer to tables of data. The display took the form of a coloured disc bearing a letter. The colour of the disc showed the locomotive's axle weight classification, which determined which routes the locomotive could work on. The letter showed the locomotive's power classification, which was used to determine the maximum load it could haul on each route. The disks were initially placed high on the cab side but were moved to a position just above the cab number plate during the Second World War to make them easier to see during blackout conditions.

GWR locomotives currently or formerly resident on the SVR were classed as follows:

Locomotive	Type	GWR Power class	BR Power class	GWR Axle load class
813	Ex-PTR	Unclassified	n/a	Unclassified
1450	1400 class	Unclassified	1P	Unclassified
1501	1500 class	C	4F	Red
2857	2800 class	E	8F	Blue
3205	2251 class	B	3MT	Yellow
3612	5700 class	C	4F by BR(W)	Blue (Yellow from 1950)
3717	3700 City class	A		Blue
4141	5101 class large prairie	D	4MT	Blue
4150	5101 class large prairie	D	4MT	Blue
4566	4500 class small prairie	C	4MT	Yellow
4930	4900 Hall class	D	5MT	Red
5164	5101 class large prairie	D	4MT	Blue
5764	5700 class	C	4F by BR(W)	Blue (Yellow from 1950)
5786	5700 class	C	4F by BR(W)	Blue (Yellow from 1950)
6634	5600 class	D	5MT	Red
6960	6959 Modified Hall class	D	5MT	Red
7325	4300 class	D	4MT	Blue
7714	5700 class	C	4F by BR(W)	Blue (Yellow from 1950)
7802	7800 Manor class	D	5MT	Blue
7812	7800 Manor class	D	5MT	Blue
7819	7800 Manor class	D	5MT	Blue

Contents

GWR route classification colours

Routes on the GWR were normally classified as "Red", "Blue", "Yellow" or "Uncoloured", according to the maximum axle load permitted by the Civil Engineer, as follows:

Colour	Maximum axle load
Red	20 Tons
Blue	17 tons 12 cwt
Yellow	16 tons
Uncoloured	14 tons

Certain routes could be modified as "dotted", for example "Dotted Blue" meant a route could be worked by "Blue" locomotives but subject to a 25mph speed restriction. Locomotives in the lower "Yellow" and "Uncoloured" classes could work the route without this additional speed restriction.

Severn Valley Railway Route Classification

During the Second World War, in order to meet wartime requirements, the line was raised from a yellow to a blue route (although restricted to engines with a maximum axle loading of 17½ tons), before eventually becoming a dotted blue route. The post-War classification and rules for working the Severn Valley Railway were set out in Section 15 of the 1948 Working Timetable as follows:

Dotted "Red" route – Hartlebury and Bewdley

Engines in the “Red” group (with the exception of the ‘King’ and the 2-8-0 47xx Class) may work between Hartlebury and Bewdley, subject to the maximum speed not exceeding twenty miles per hour at any point, also to strict adherence to the following prohibitions and restrictions.

"Dotted "Blue" route – Bewdley and Iron Bridge and Broseley

Engines in the “Blue” group (with the exception of the 2-8-0 types) may work between Bewdley and Iron Bridge and Broseley, inclusive, at a maximum overall speed not exceeding 25 miles per hour at any point, subject to the following prohibitions and restrictions.

"Blue" Route – Buildwas and Shrewsbury

Engines in the “Red” group (with the exception of the ‘King’ and the 2-8-0 47xx Class) may work over the running lines only between Buildwas and Shrewsbury, provided the speed does not exceed 20 miles per hour at any point and subject to service restrictions.

John Marshall’s history of the Severn Valley Railway also states that special rules applied to 51xx and 81xx ‘large prairies’, which were subject to a 25mph restriction between Victoria Bridge and Linley.

The maximum permitted line speed between Hartlebury and Shrewsbury was 50mph. The additional prohibitions and restrictions referred to mainly related to sidings and weighbridges, although there were details restrictions on the working of locomotives over Victoria Bridge.

Kidderminster to Woofferton Route Classification

Information on the Kidderminster to Bewdley Loop line and the Tenbury Branch was included in Section 12 of the 1948 Working Timetable, as follows:

Kidderminster and Bewdley

Any engine in the “Red” group (excluding the ‘King’ class and the 2-8-0, 47xx Class) may work between Kidderminster and Bewdley subject to the maximum overall speed not exceeding 20 miles per hour.

Bewdley and Woofferton. (Dotted Blue)

Engines in the “Yellow” group may work between Bewdley and Woofferton subject to service and special speed restrictions.

Engines in the “Blue” group are authorised to work between Bewdley and Woofferton at a maximum speed of 25 miles per hour subject to the following prohibitions and service speed restrictions.

As with the Severn Valley Branch, the overall line speed was limited to 50 mph, while the prohibitions and restrictions mainly related to sidings and weighbridges.

GWR locomotive power classification

The GWR allocated locomotives into power classes ranging from Ungrouped (lowest), A to E (highest), and Special (King class) as follows:

Power class	Tractive effort (lb)
Special	Over 38,000
E	33,001 – 38,000
D	25,001 – 33,000
C	20,501 – 25,000
B	18,501 – 20,500
A	16,500 – 18,500
Ungrouped	Below 16,500

For each route, the working timetable included a table of locomotive classes and the maximum permitted load. For example the 1948 working timetable specified that a ‘small prairie’ such as 4566 was limited to a load of 310 tons between Hartlebury and Shrewsbury, although a load of 335 tons was permitted for “trains liberally timed”. The power classes and loads did not differentiate between Passenger, Freight and Mixed traffic working.

After nationalisation

During the Second World War the LNER developed a somewhat more sophisticated version of the GWR's route availability classification system which was adopted by BR after nationalisation. Route Availability was based on classes RA 1 to RA 10 and took into account the weight per foot length of a locomotive rather than just the simple axle loading used by the GWR. BR also adopted the LMS classification system for locomotive power based on classes 0 to 9 with distinctions made for Passenger, Freight and Mixed Traffic.

However in BR's Western Region, the old GWR system continued in use until after the Severn Valley Branch closed in 1963, with BR locomotive classes being allocated the relevant GWR route colours. For example a BR Standard Class 4 tank engine such as 80079 was given the general BR classification of axle load class RA5 and power class 4MT. Within BR(W) the route availability became "Class 4 (2-6-4T) (80XXX): Prohibited on 'Yellow' and 'Uncoloured' routes. Restrictions – as for 'Blue' engines.".

One result of BR's new method of assessing weight restrictions without solely relying on axle weight was that the 5700 class pannier tanks were reclassified from "Blue" to "Yellow" by BR(W) in 1950. The reason given was the low 'hammer blow' that the class produced, which reduced the wear on the track.

Preservation

When the SVR began operations in 1970, the line was still subject to the 17 tons 12 cwt axle weight restriction. This meant that large locomotives such as 61994 The Great Marquess could not be used until a program of upgrading the line had been undertaken. The successful completion of this means that the SVR has since hosted a GWR 'King' class locomotive, as well as similar classes of locomotives from other companies. However sections of the line such as Victoria Bridge remain subject to operating procedures which restrict the double-heading of locomotives.

The Light Railway Order under which the SVR operates specifies a maximum speed of 25mph for normal services. Operation up to 50mph may be carried out between Kidderminster and Bewdley when the railway is closed to the public; a recent example being the testing of Metropolitan Railway 0-4-4T No 1 in 2012 prior to its participating in the London Underground events in 2013.

See also

• Steam Locomotives
• Locomotives used on the Severn Valley Branch in commercial service
• Great Western Railway

Links

GWR Power and Weight Classifiation on Wikipedia
Route availability on Wikipedia
1948 BR(W) Working Timetables on Michael Clemens' website (Section 15 includes the Severn Valley Branch, Section 12 includes Kidderminster to Woofferton)