Meaning of “im dritten”

Question

From Der Spiegel:

Genscher schafft es tatsächlich, die Stimmung zu drehen und die Menschen im Botschaftsgarten zu beruhigen. Busse bringen die Flüchtlinge zum Prager Bahnhof Liben, der erste Zug geht um 21.00 Uhr.

Diplomat Elbe ist im dritten dabei: „Ich habe den Leuten gesagt, dass ich die vertrauensbildende Maßnahme sei“ berichtet er. „Und ich habe auch darum gebeten, sich nicht provozieren zu lassen.“

What is the meaning of im dritten here? Is it that Elbe is the third person to speak? (I’ve tried searching both the dictionary and Google, but neither helps much with a generic phrase like this.)

Answer 1

It’s the third train that is meant here. The subclause

[…] der erste Zug geht um 21.00 Uhr.

can be translated with

the first train leaves at 9 pm.

and implies that there are several trains leaving. The first sentence in the next paragraph refers to those trains. Diplomat Elbe is in the third one. I have to admit that I had to read the quote several times before getting its meaning, it’s not easy to understand.

Answer 2

I think, from the text in the question, it is not clear if im dritten refers to trains or busses (cf comment of @chris under the answer of @Deve).

However, I checked the original articel and in the sentences before it becomes clear:

Ursprünglich wollten er [Genscher] und Seiters sich in die ersten beiden Züge setzen, aber das lehnt die DDR ab. Stattdessen sollen nun die Begleiter der Minister in den rumpelnden Waggons der (Ost-)Deutschen Reichsbahn mitfahren.

can be translated as:

Initially, he [Genscher] and Seiters wanted to take the first two trains, but the GDR refused. Instead the attendants of the ministers should accompany the people in the rumbling waggons of the East German railway.

(from the context: the rumbling waggons of the East German railway are the third train)