"closing speed" meaning in English

{
  "forms": [
    {
      "form": "closing speeds",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "closing speed (plural closing speeds)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "If two vehicles, both travelling at 70 mph (miles per hour), collide head-on, their closing speed is 140 mph.",
          "type": "example"
        },
        {
          "ref": "2021 February 24, Greg Morse, “Great Heck: a tragic chain of events”, in RAIL, number 925, page 39",
          "text": "This secondary collision, head-on with a closing speed of 142mph, caused the DVT to veer off to the left. Many of the coaches behind it overturned and careered into an adjacent field.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "The speed of a moving object relative to another object which it is approaching."
      ],
      "id": "en-closing_speed-en-noun-v8GE1BuM",
      "links": [
        [
          "relative",
          "relative"
        ]
      ]
    }
  ],
  "word": "closing speed"
}

{
  "forms": [
    {
      "form": "closing speeds",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "closing speed (plural closing speeds)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "English terms with usage examples"
      ],
      "examples": [
        {
          "text": "If two vehicles, both travelling at 70 mph (miles per hour), collide head-on, their closing speed is 140 mph.",
          "type": "example"
        },
        {
          "ref": "2021 February 24, Greg Morse, “Great Heck: a tragic chain of events”, in RAIL, number 925, page 39",
          "text": "This secondary collision, head-on with a closing speed of 142mph, caused the DVT to veer off to the left. Many of the coaches behind it overturned and careered into an adjacent field.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "The speed of a moving object relative to another object which it is approaching."
      ],
      "links": [
        [
          "relative",
          "relative"
        ]
      ]
    }
  ],
  "word": "closing speed"
}