Underground Rennes

Statistics and visualisation of Rennes's underground

1. Introduction

The purpose of this study is to give some basic information about the underground in Rennes. The data are coming from the data platform of Rennes Métropole (link to data) queried in May 2019. The visualisation is done with the python library "bokeh".

Map 1: Underground railway tracks and stations

2. Statistics and analysis

Rennes has one underground line (line a) since 2002. This line transports about 140,000 passangers daily. A second line (line b) is currently being built which opening is planned for 2020.

2.1. Underground stations analysis

Table 1: Stations key numbers

	Line a	Line b
Number of stations	15	15
Terminal 1	J.F. Kennedy	Saint-Jacques-Gaité
Terminal 2	La Poterie	Cesson Viasilva
euclidean distance...	...	...
Between terminals	6.2 km	7.6 km
Average between 2 stations	583 m	800 m
Median between 2 stations	552 m	776 m
Minimum between 2 stations	378 m Charles de Gaulle - Gares	535 m Saint Germain - Sainte Anne
Maximum between 2 stations	782 m Gares - Jacques Cartier	1,116 m Cleunay - Mabilais

The euclidean distance is the shortest distance between 2 points. The railway track length is at least equal to the euclidean distance. The railway path does not always follow a straight line because of various constraints.

Figure 1: Distribution of euclidean distance between 2 stations

Both underground lines have the same amount of stations (15), however the line b is longer than the line a by 1.4 km (+22.6%). The average, minimum and maximum euclidean distances between 2 stations are higher for line b compared to line a. The figure 1 highlights the wider gap between stations of the line b.

2.2. Analysis of the railway path

Table 2: Railway path key numbers

Length	Line a	Line b	Difference (a-b)
Total	9,696 m	13,727 m	-4,031 m (-42%)
Between terminals	8,587 m	12,949 m	-4,362 m (-51%)
Tunnel	3,680 m	8,062 m	-4,382 m (-119%)
Covered trench	3,030 m	1,782 m	1,248 m (+41%)
Viaduct	945 m	2,077 m	-1,132 m (-120%)
Station	537 m	919 m	-382 m (-71%)
Transition zone	395 m	109 m	286 m (+72%)

The total railway path is made of non commercially used portions, these portions are used for maintenance and services. They represent for the line a and the line b respectively 11.4% and 5.6% of the total length. The line b is longer than the line a by about 50%. The tunnel portions of both lines are almost equivalent between the line a (8,587 m) and the line b (8,062 m). The number of stations is same for both lines. however, the length of station railways is longer for the line b by about 30%.

Figure 2: Distribution of railway length by type

Figure 3: Comparison between euclidean and real railway distances between 2 stations

The closest a point is to the green line and the closest the railway path length is to the euclidean distance. No points can be above the green line. It is impossible to have a railway path length shorter than the euclidean distance (which is the shortest distance between 2 points). This figure shows that the railway tracks between 2 stations of the line a are closer to the green line than those of the line b.

3. Visualisation

Map 2: Localisation of underground stations

Both lines are crossing twice at the stations Gares and Saint-Anne. The line a goes across town following the axis North-East South-East while the line b follows the axis South-West North-East.

Map 3: Railway lines path

The railway paths highlight the winding shape of the lines and explains the difference between the euclidean distance and the real railways length between the stations. For example, between the stations Jacques Cartier and Clémenceau (line a) the difference is 0 m and the railway tracks are almost straight. Opposite case between the stations Gares and Saint-Germain (line b) the difference is 320 m and the railway path has along curve.

Map 4: Railway lines path by type

This map emphasizes the different kind of railway tracks. In town centre, there is almost exclusively tunnel due to the high density. Moving away from the centre, covered trenchs are more often used as well as viaduct more used at the end of lines.

4. Spatial analysis

This analysis focuses on the density population compared to the stations localisation. Density data have been downloaded for 200m square side (link to data). This dataset is not complete as the total population from the data is 172,560 inhabitants while the total population of the city is about 215,000 inhabitants (2018). It can be seen on the map 5 below which areas are missing data.

Map 5: Population density

The colors have been chosen based on the population density quartiles:
- 25th percentile: 77 pop/km²
- 50th percentile: 245 pop/km²
- 75th percentile: 760 pop/km²
It can be seen from map 5 the higher density in city centre and some other areas with high building like in the South.

Map 6: Proximity to stations

A buffer zone of 500m radius is displayed on map 6. This buffer zone represents 14.3 km² which is about 28% of the total area of Rennes (50.38 km²).

Map 7: Population density and proximity to stations

Both maps 5 and 6 are combined to highlight the localisation of the stations with the population density. With the population data used, 113,871 inhabitants are living within 500m to an underground station. It represents about 66% of the population for the data available. Considering the total population estimated around 215,000 inhabitants it still represents at least about 50% of the population living at 500m or less to a station. Only the population of Rennes is taken into account while some stations of the line b are in neighbours cities(i.e. South-West and East).