For full context:
<https://www3.nhk.or.jp/news/html/20180617/k10011481821000.html?utm_int=news_contents_news-
main_001>

The sentence in question:
ＪＲ東日本によりますと、17日午後２時前、午後０時20分に東京を出発し、新函館北斗に向かっていたはやぶさ21号と秋田に向かっていたこまち21号が、宮城県の仙台と古川の間を走行中に非常ブレーキが作動し、緊急停車しました。

My attempt at translation: "According to JR east Japan, on the seventeenth
before 2p.m (??? 午後０時20分に ???), the hayabusa21 which left tokyo and headed
towards shinhakodate-station and the komachi21 which headed towards Akita had
an emergency break while in motion through the area of an old river and Sendai
City in miyagi prefecture."

So 走行中 is listed as a の-adjective
<https://jisho.org/search/%E8%B5%B0%E8%A1%8C%E4%B8%AD> but my textbooks never
told me that に can be applied to them ^^ I guess it does the same thing as
with な-adjectives? Making them an adverb? I could imagine interpreting に very
fundamentally as "in" like "in motion", however then it would only reinforce
the basic meaning of 走行中 and furthermore, there is a preceding を. This を
reminds me of the を you can see in 橋を歩く for example, but I'm not sure wether I
can put it into relation to the 非常ブレーキが作動し phrase since that one seems rather
isolated to me...
CC BY-SA 4.0
2018-06-18T20:26:55.580
59565
2018-06-18T22:15:25.430
20172
question
grammar
How does this に in 走行中に work here?
```

    How does this に in 走行中に work here?
    
```

As @user4092 mentioned, に can be used to denote a point in time or a duration
of time. Also, ○○中 can be used to denote a time period during which ○○ is
happening. Therefore, ○○中に functions as an adverb, and ○○中の functions as an
adjective.

```

    furthermore, there is a preceding を
    
```

This is similar to the を in the `橋を歩く` that you mentioned.

`を`refers to `走行` in `（宮城県の仙台と古川の）間を走行（する）`. This means "travel the interval
between Sendai and Furukawa".

So,

> 「．．．はやぶさ21号と．．．こまち21号が、仙台と古川の間を走行中に．．．」

means (omitting the words represented by ellipses)

> ...while Hayabusa 21 and Komachi 21 were traveling between Sendai and
> Furukawa...
CC BY-SA 4.0
2018-06-18T22:15:25.430
59567
2018-06-18T22:15:25.430
29590
59565
answer