Update section on trains.

Didier BARRET
1 parent a26c53f7
Showing 1 changed file with 22 additions and 11 deletions Show diff stats
content.yml
@@ -333,7 +333,8 @@ home:
       - title: What does the tool do?
         content: |
           The tool computes the carbon footprint associated with round
-          trip flights, considering only the emission associated with the flight. 
+          trip flights, considering only the emission associated with the flight
+          (i.e. do not include life cycle emissions).
           It does so for a set of trips from a given city of origin
           to a set of destinations. Similarly, the tool allows to compute 
           the carbon footprint of a larger set of trips, corresponding to a 
@@ -399,7 +400,8 @@ home:
           distance intervals. For its carbon compensation service, KLM 
           provides on its web site a table of emissions for a large range 
           of flights. The KLM data have been also been fitted with linear 
-          functions. 
+          functions. Differences up to a few tens of percent may be found between
+          the estimates and the linearly interpolated values. 
  
       - title: What about radiative forcing?
         slug: rfi
@@ -450,20 +452,29 @@ home:
           is an input to be selected by
           the user (it is set to 300 km by default). Below the minimum 
           distance for flying, it is assumed that train is used. The tool 
-          then computes the travel footprint associated with train. The 
-          French emission factors provided by ADEME are 3.37 and 5.11 
-          grams of carbon dioxide equivalent per km per passenger for 
+          then computes the travel footprint associated with train (as 
+          for flight emissions, the computation does not include 
+          life cycle emissions). The French emission factors provided by 
+          ADEME are 3.37 and 5.11grams of carbon dioxide equivalent per km per passenger for 
           high speed trains and normal trains respectively. This low value is 
           due to the fact that electricity is provided by nuclear plants. It 
           is larger by some factors across Europe. The tool thus assumes the 
           mean of the emission factors of national and international rails, 
           as provided by DEFRA (i.e. 23 grams per passenger km). This 
-          makes the carbon dioxide equivalent emission of trains, typically 5-10% 
-          of the one of aircrafts. It is worth relating a distance 
-          traveled by train to a duration. In Europe, the average speed 
-          of trains is about 100 km/hour, meaning that it takes about 5 
-          hours to travel by trains between two cities with a 
-          great circle distance of 500 km.
+          makes the carbon dioxide equivalent emission of aircrafts 
+          10 to 20 times more than the one of trains. Some may select train 
+          traveling instead of flying based on the duration of the trip.
+          It is thus worth relating the minimum distance for flying to 
+          a travel time duration by train. In Europe, from a shallow survey of trip 
+	      durations between major cities, it appears that the average speed 
+          of trains is about 100 km/hour. This means that on average it takes about 5 
+          hours to travel by train between two cities with a 
+          great circle distance of 500 km (including connexions, 
+          deviations from the shortest paths…). 100 km/hour may be on the 
+          low side by a couple of 10 km/hour in 
+          countries where high speed trains are frequently used, 
+          and on the high side by the same amount in countries where high speed 
+          trains are less available or not available at all. 
  
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